Without limiting the scope of the present invention, its background is described with reference to constructing a subterranean well, as an example.
In conventional practice, the drilling of an oil or gas well involves creating a wellbore that traverses numerous subterranean formations. For a variety reasons, each of the formations through which the well passes is preferably isolated. For example, it is important to avoid an undesired passage of formation fluids into the wellbore and an undesired passage of wellbore fluids into a formation. In addition, it is important to prevent fluids from producing formations to enter or contaminate non producing formations.
To avoid these problems, conventional well architecture includes the installation of heavy steel casing within the wellbore. In addition to providing the isolating function, the casing also provides wellbore stability to counteract the geomechanics of the formations such as compaction forces, seismic forces and tectonic forces, thereby preventing the collapse of the wellbore wall.
In typical wellbore construction, after an upper portion of a well has been drilled and a casing string installed therein, drilling recommences to extend the well to the next desired depth. In order to allow passage of the drill bit and other tools through the previously installed casing string, each successive section of the well is drilled with a smaller diameter than the previous section. In addition, each succeeding casing string placed in the wellbore has an outside diameter smaller than that of the previously installed casing string.
The casing strings are generally fixed within the wellbore by a cement layer between the outer wall of the casing and the wall of the wellbore. When a casing string is located in its desired position in the well, a cement slurry is pumped via the interior of the casing, around the lower end of the casing and upwards into the annulus. As soon as the annulus around the casing is sufficiently filled with the cement slurry, the cement slurry is allowed to harden. The cement sets up in the annulus, supporting and positioning the casing and forming a substantially impermeable barrier.
In one approach, each casing string extends downhole from the surface such that only a lower section of each casing string is adjacent to the wellbore wall. Alternatively, the wellbore casings may include one or more liner strings which do not extend to the surface of the wellbore but instead typically extend from near the bottom end of a previously installed casing downward into the uncased portion of the wellbore. Liner strings are typically lowered downhole on a work string that may include a running tool that attaches to the liner string. The liner string typically includes a liner hanger at its uphole end that is mechanically or hydraulically set. In one example, an expansion cone is passed downwardly through the liner hanger to radially expand and plastically deform the liner hanger into sealing and gripping engagement with the previously installed casing string.
It has been found, however, that once the expansion cone has passed through and plastically deformed the liner hanger, resilience in the casing string and the liner hanger may result in a reduction in the inner diameter of the liner hanger. When such inner diameter reduction occurs, retrieval of the expansion cone back through the previously set liner hanger may be difficult. Accordingly, a need has arisen for an expansion cone that is operable to plastically deform the liner hanger into sealing and gripping engagement with the casing string. A need has also arisen for such an expansion cone that is operable to be retrieved through the liner hanger even after resilience in the casing string or the liner hanger reduces the inner diameter of the liner hanger after setting.